Inhibition of Ubiquitin Phosphorylation by Nucleoside Analogues

The phosphorylation of ubiquitin by the mitochondrial protein kinase PINK1, upon mitochondrial depolarization, is an important step in the repair and recycling of the mitochondria via mitophagy. As mutations in PINK1 can cause early-onset Parkinson’s disease (PD), there has been a growing interest in small molecule modulators of PINK1-mediated mitophagy as potential PD treatments. In this work, we show that in HeLa cells, primary mouse fibroblasts and astrocytes, N6-substituted adenosines, such as N6-(2- furanylmethyl)adenosine (known as kinetin riboside) and N6-benzyladenosine, inhibit ubiquitin phosphorylation that is induced by established mitochondrial depolarizing agents, CCCP and niclosamide. Although these nucleoside analogues inhibited niclosamide- and CCCP-induced ubiquitin phosphorylation, they did not prevent the mitochondrial membrane depolarization. Notably, treatment of cells with these nucleoside analogues alone induced low level mitophagy and did not cause mitochondrial fragmentation. Together, this work presents N6-substituted adenosines as new inhibitors of CCCP- and niclosamide-induced PINK1-mediated ubiquitin phosphorylation and highlights their potential utility in treating aged and sporadic PD as well as Lewy body dementia patients who have elevated levels of phosphorylated ubiquitin.